1. Field of the Invention
The present invention relates to method of controlling toner density detection in an electrophotographic-type image forming apparatus such as a copying machine, printer, facsimile device, etc.
2. Description of the Background
Generally, in an electrophotographic-type image forming apparatus such as a copying machine, printer, facsimile device, etc., the image forming process is carried out in such a manner so that a photosensitive body including a drum-shaped photosensitive body, a belt-shaped photosensitive body, or the like, is rotated by a motor, an electrostatic latent image is formed by performing a uniform charging and an image is exposed on the photosensitive body by use of latent image forming means including charging apparatus and exposing means. The electrostatic latent image is converted to a visible toner image by developing the latent image by a developing apparatus, and the toner image thus formed is transferred onto copying paper supplied from a paper supplying apparatus by use of a transferring apparatus. The transferred toner image is fixed on the paper by use of a fixing apparatus, and the photosensitive body is cleaned by a cleaning apparatus after transferring the toner image.
And further, regarding such an electrophotographic-type image forming apparatus, a method of making the time interval of the image forming process (approximately same as that of the transferring process) longer than the standard interval when the toner density becomes equal to or lower than a predetermined level has already been described in the published patent specification of Japanese Laid-open Patent Publication No. 63-243980/1988. Furthermore, in the above-mentioned electrophotographic-type image forming apparatus, another method of delaying the timing of supplying the copying paper or temporarily stopping the image forming operation when the density of toner employed as developing agents accommodated in the developing apparatus is described in the published patent specifications of Japanese Laid-open Patent Publication Nos. 63-287978/1988, 63-287979/1988, 63-287980, etc.
In the recent years, in the electrophotographic-type image forming apparatus represented by the copying machine, a transferring belt apparatus including a resilient endless belt made of a resistor having a medium resistance value generating a small amount of ozone and capable of performing preferable transferring over entire copying paper has been utilized. The above transferring belt apparatus includes a transferring belt contacting with and detaching from the photosensitive body by action of the driving portion's rotational driving and transferring bias applying means for applying the transferring bias voltage to the transferring belt. At the time of transferring, the transferring belt comes into direct contact with the photosensitive body, and the transferring bias voltage is applied to the transferring belt from the transferring bias voltage applying means, so that the toner image on the photosensitive body is transferred onto the copying paper passing through the nipping portion between the transferring belt and the photosensitive body.
And further, in relation to the method of detecting the toner density in order to control the density of toner employed as the developing agents in the developing apparatus, there has been adopted a method of employing the combination of an optical sensor (called a "P-sensor", hereinafter) for detecting the reflection density of a standard density pattern (called "P-sensor pattern", hereinafter) formed on the photosensitive body and a magnetic sensor (called a "T-sensor pattern", hereinafter) for assuming the toner density by detecting the magnetic permeability of the developing agents accommodated in the developing apparatus. Conventionally, the P-sensor has been disposed at the downstream side of the developing apparatus. However, in order to avoid a defect caused by the dispersing toner from the developing apparatus, the P-sensor is disposed preferably at the lower portion of the cleaning apparatus, namely, at the downstream side of the transferring belt apparatus, instead of the downstream side of the developing apparatus.